Re: [fluka-discuss]:

From: Paola Sala <>
Date: Sun, 31 Jan 2016 12:07:03 +0100

Dear Pedro,
am I understanding correctly that you wish to count the number of NEUTRINO
interactions in the water tank? If this is the case, the answer is ..very
simple, you'll get one neutrino interaction per primary neutrino. I copy
here a few sentences from the relase notes:

*Neutrino interactions are activated in "forced mode" : when a neutrino
primary particle is requested, the code forces a neutrino interaction to
occur in the point (or area) defined in the BEAMPOS card.
* the interaction rate does not depend on the neutrino energy. This means
that if the user requests a momentum spread in the BEAM card, all neutrino
momenta are sampled with the same probability, disregarding the momentum
dependency of the total interaction cross section.

* Only interactions by neutrinos as primary particles are considered.
Secondary neutrinos do not (re)interact.

The reason is that fluka has pretabulated neutrino-nucleon cross
sections vs energy, but it does not have pretabulated neutrino-nucleus
cross sections.

If your aim is to extract the neutrino cross section as a function of
energy, you'll need to dig the information from the fluka common blocks.

I'll try to explain how at the end of this email, first i'll give answer
to your various points.
(1) Detect scores the spectrum of energy deposition: each "channel"
content is the number of events depositing an energy E_i, E_i being
defined by your requested energy limits and by the number of channels. (2)
Usrbin can score either fluence or energy deposition, and, yes, as a
function of space.
(3) probably means that you gave the beam position ( BEAMPOS card ) in
vacuum, and, as said before, neutrinos are forced to interact in the
BEAMPOS position.
(4) The DISCARD card needs every particle one bey one. However, you can
kill all electromagnetic with EMF , sdum EMF-OFF, and use the PART-THR
card to stop all the others immediately. PART-THR accepts ranges of

(5) this is in our plans. However, most of your questions have their
answer in the manual, in the release notes, in the materials from the

Coming back to your primary question:
Neutrino-nucleus interactions are sampled according to a MAXIMIZED cross
section, that allows to accomodate for cross section variation due to
fermi motion.
Then, interactions are kept or rejected according to the actual target
fermi momentum an to possible Paul blocking. (if you need an introduction
about sampling and sampling by rejection you can have a look at the
corresponding lecture in the fluka course material). The number of
rejection at each interaction is kept track of.
In practice, you should edit the mgdraw.f user routine.
Include two relevant common blocks:
In The USDRAW entry, chech that the interaction is inelastic (ICODE=101)
and produced by a neutrino (JTRACK variable, common TRACKR). At each
interaction, you'll get the maximized cross section STNUSC an the inverse
of the number of trials OPACTY. The true cross section can be calculated

true cross section =STNUSC * number of events / (sum of 1./OPACTY over

for instance, at each event (NCASE is the event counter).
         in the header: SAVE SUMO
         in USDRAW
         IF (NCASE .EQ. 1 ) SUMO = ZERZER

 Explaination, discussion end examples on how to use user routines are in
the manual and in the material of the advanced fluka courses (links from
the web site)

Please read the fluka license about the use of basic data extracted from
Hope this helps
> Dear Flukas,
> I am trying to simulate a neutrino beam detection on a water tank using
the FLAIR. And I need to obtain the number of collisions as a function of
> energy as my estimator, unfortunately I am not sure what card I should
> to do that.
> (1) I've tried to use the DETECT card but it printed a table with energy
range and two other columns that I don't know what they are but doesn't
seems to be particle counting due to the fact it has results less them 1.
> (2) The USRBIN does not seems right either because it prints the fluence
(not number of particles) and is a spatial function not energy.
> (3) I've tried to run electrons to test and them neutrinos, when I ran
electrons I get the files, but when I run neutrinos (even if I undiscad
them) I get the error:
> Abort called from FLDFSR reason FORCE INTER. IN VACUUM Run stopped!
> Is this due to the fact that there was no neutrino interaction due to
> small cross section or is it some other error?
> (4) Is it possible to automatically DISCARD all the particle trackings
> neutrinos (since I only need the collision event)? It seems a waste of
processing keeping track of every particle when I don't need it, but on
the CANCEL card it seems to me that I have to do it manually for every
single particle.
> (5) Isn't it better to have a stack exchange-like forum for the fluka
project instead/together of/with email listing, so that people can find
solutions to the problems that were already asked?
> Thanks a lot,
> Pedro
> __________________________________________________________________________
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Paola Sala
INFN Milano
tel. Milano +39-0250317374
tel. CERN +41-227679148

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Received on Sun Jan 31 2016 - 13:42:55 CET

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